1. Field of the Invention
The present invention relates to a thermosensitive recording material for plate-making use which is useful as a block copy for making a printing plate for flexography, gravure printing, offset printing, and screen printing. In addition, the present invention relates to a thermosensitive recording material useful as a recording material for computer-aided design (CAD). Further the present invention relates to a block copy sheet for making a printing plate, and a printing plate prepared by using the block copy sheet.
2. Discussion of the Background
Thermosensitive recording materials are widely known which utilize a coloring reaction between an electron donating coloring compound (hereinafter sometimes referred to as a coloring agent) and an electron accepting compound (hereinafter sometimes referred to as a color developer). In recent years, the thermosensitive recording materials are used for various uses, and needs exist for thermosensitive recording materials which can be used as second original sheets or plans for diazo copying. In addition, needs exist for thermosensitive recording materials which can be used as a block copy film for making a plate useful for flexography, gravure printing, offset printing, and screen printing.
In general, the characteristics requisite for the thermosensitive recording materials are as follows:
1) recorded images formed therein have high contrast between image areas and background areas (good image recognizability);
2) recorded images have good light shielding properties and background areas have good light transmitting properties against an ultraviolet wavelength region (360 nm-420 nm) so as to be used as a block copy film for plate-making use;
3) the thermosensitive recording sheets or films and recorded images have good preservation stability even when preserved under various environmental conditions such as high temperatures and high humidity, and good light resistance;
4) recorded images can be easily checked when determining whether there are deviation and mistakes in the images while several block copy films for plate-making use are overlaid each other (good drawing-checking ability);
5) recorded images have good dimensional accuracy;
6) recorded images have good resolution; and
7) the thermosensitive recording films have good head-matching properties when images are recorded with a thermal head.
A thermosensitive recording material having such requisite properties is proposed in Japanese Laid-Open Patent Publication No. 8-118811. However, when a block copy film is prepared for plate-making uses, there is a case in which high levels of inter-plates accuracy between block copy films (this accuracy is sometimes referred to as inter-plate error) and skew are required. Therefore problems concerning the inter-plates accuracy and skew occur when the above-proposed thermosensitive recording material is used as the block copy. As shown in FIG. 1, the term xe2x80x9cinter-plates accuracyxe2x80x9d is defined as the length difference, (La-Lc) and (Lb-Ld), and the term xe2x80x9cskewxe2x80x9d is defined as the length difference (La-Lb) and (Lc-Ld).
With respect to the above-mentioned problems concerning the inter-plates accuracy and skew, the dimensional accuracy of recorded images formed in a block copy film depends on the conditions under which the block copy film is prepared and the printing conditions under which the formed block copy film is used for printing. When a block copy film is prepared using a block copy forming apparatus, the block copy forming apparatus also has influence on the dimensional accuracy of the block copy film, which are as result-effecting as or more result-effecting than the influence that the film has on the dimensional accuracy. For example, the accuracy of film-feeding and the dimensional accuracy of heating elements of a print head such as thermal heads have influence on the dimensional accuracy of the resultant images.
The accuracy of film-feeding is influenced by:
(1) uneven feeding which is caused by the friction between the surface of the film and a thermal head serving as a print head, fusion of the film to the thermal head (a so-called sticking phenomenon, i.e., a phenomenon in which the surface of a recording material is softened or fused by the heat of a thermal head and sticks to the thermal head), and head-dust adhered to the thermal head due to the fusion of the film (so-called head-dust adhesion);
(2) simple mechanical feeding accuracy of the film fed by an image forming apparatus, which is caused by changes of environmental conditions and inner temperature of the image forming apparatus; and
(3) simple physical expansion and contraction of the film caused by changes of environmental conditions and inner temperature of the image forming apparatus.
The sticking phenomenon and the head-dust adhesion caused by fusing-adhesion largely depend on the protective layer (or the overcoat layer) and the recording layer. Even when only the lubricating property of the protective layer is enhanced and the film of the protective layer is hardened, if the recording layer is a layer which softens and is crushed upon application of heat, the recording layer becomes the cause of the sticking phenomenon and the head-dust adhesion caused by the fusion of the film.
In addition, changes in feeding quantity due to changes of environmental conditions and the temperature inside the apparatus, and expansion and contraction of the film due to the temperature change are a factor of the feeding accuracy. Further, changes in tension when a roll-shaped film is fed out, which is caused by charging of the roll film and changes of the diameter of the roll, are a factor of the feeding accuracy.
There is a technique, which is disclosed in Japanese Laid-Open Patent Publication 10-166737, for improving the above-mentioned problems. However, even when this technique is used, there occurs a problem in the dimensional accuracy, which is caused by reasons other than the above-mentioned reasons.
Because of these reasons, a need exists for a thermosensitive recording material which utilizes a color reaction between an electron donating coloring compound and an electron accepting compound and which can solve the problems which have been experienced in the past.
Accordingly an object of the present invention is to provide a thermosensitive recording material which utilizes a color reaction between an electron donating coloring compound and an electron accepting compound and which can produce high levels of inter-plates accuracy between block copy films for plate-making use and skew.
Another object of the present invention is to provide a block copy sheet capable of making a good printing plate.
Yet another object of the present invention is to provide a printing plate for flexography, gravure printing, offset printing, and screen printing, which can produce good print images.
To achieve such objects, the present invention contemplates the provision of a roll-shaped thermosensitive recording material having a thermosensitive recording layer, which includes an electron donating coloring compound, an electron accepting compound and a binder resin and which is formed overlying a roll-shaped substrate, wherein the variation (R) of thickness of the roll-shaped thermosensitive recording material in the lateral direction is not greater than 3 xcexcm.
The term roll-shaped recording material means a flat strip of recording material which is rolled up.
In another aspect of the present invention, a roll-shaped thermosensitive recording material is provided in which a thermosensitive recording layer including as main components an electron donating coloring compound, an electron accepting compound and a binder resin is formed overlying a substrate and in which the difference (inclination) in thickness between the right side and the left side thereof is not greater than 0.7 xcexcm.
The thermosensitive recording material of the present invention may have an overcoat layer, which is formed overlying the thermosensitive recording layer and which includes as a main component a resin having almost the same refractive index as the binder resin included in the thermosensitive recording layer.
The variation (R) of thickness of the roll-shaped substrate in the lateral direction is preferably not greater than 4 xcexcm, and the difference (inclination) in thickness between the right side and the left side of the roll-shaped substrate in the lateral direction is preferably not greater than 0.6 xcexcm.
The thermosensitive recording material of the present invention, in which images are recorded upon application of heat or the like, is preferably used as a block copy for making a plate for flexography, gravure printing, offset printing, and screen printing.
These and other objects, features and advantages of the present invention will become apparent upon application of the following description of the preferred embodiments of the present invention taken into conjunction with the accompanying drawings.